Strand-like material, such as yarn, that is to be used as pile in cut pile carpets typically is prepared by cabling ("ply-twisting") together two or more single strands, heatsetting them with hot air and/or steam in their twisted condition, and finally drying them. The strands are heatset in the ply twisted configuration so that when the strands are tufted into carpet and cut, the plies will remain in their twisted condition without separating and matting during wear.
One known method of heatsetting a strand-like material involves passing the strand-like material through a Superba.RTM. continuous heatsetting machine. Generally, in the operation of a Superba heatsetting unit, the strand-like material is laid in loops on a conveyor belt that first moves through an atmospheric steam prebulker and then through a heating zone. In the prebulker, the strand-like material is heat relaxed to develop bulk in the material. In the heating zone, the strand-like material is treated with pressurized, saturated steam that is maintained at a high temperature according to the type of material to heatset the twist. Another known method involves passing the strand-like material through the heating zone of a Suessen continuous heatsetting machine. The Suessen unit treats the strand-like material with dry heat to heatset the twist.
While in the heating zone, it has been found that non-uniform conditioning to the strand-like material may occur. The non-uniform conditioning leads to irregularities such as, for example, streaking and chevroning in a subsequent dyeing operation. For example, high bulk and high shrinkage of yarn while in the heating zone cause the mass of the yarn on the belt to become too dense to be heatset uniformly. When the yarn is then made into a carpet during a standard tufting operation and dyed using conventional dyeing equipment, visual examination reveals a non-uniform appearance, for example, streaks and chevrons, in the dyed carpet.
While some improvement in carpet uniformity may be seen by reducing yarn speed, the result is low productivity, which is not cost effective. Increasing yarn speed to increase productivity, however, decreases the dwell time in the heating zone, which results in carpet non-uniformity. Another problem with high throughput speeds is the propensity of the strand-like material to tangle. Once this occurs, the machine must be shut down and allowed to cool before the material may be untangled.
The Superba.RTM. TVP2S heatsetting machine has increased belt width and coiler diameter (both increased from 200 mm to 260 mm). While these modifications improve machine throughput of strand-like material, they do not address the problems of productivity and carpet uniformity. An additional limitation is that fact that one would have to buy this new equipment at significant cost as opposed to modifying existing equipment at a significantly lower cost.
A method and apparatus for overcoming the non-uniform conditioning of strand-like material while increasing throughput and productivity is, therefore, desired.